Chapter 3, Problem 40P

Interpretation Introduction

Interpretation: The relative reactivity of hydrogens in $90{\text{ \% CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CHBr}}_2$ , $8.5{\text{ \% CH}}_{\text{3}}{\text{CHBrCH}}_2\text{Br}$ and $\text{1}{\text{.5 \% BrCH}}_2{\text{CH}}_2{\text{CH}}_2\text{Br}$ formed should be calculated and compared with similar results of bromination with propane.

Concept introduction: The monobromination performed with ultraviolet light proceeds via radical chain mechanism.

Tertiary $\text{C – H}$ bonds react in halogenations more readily than secondary those in turn are faster to react than primary. This can be attributed to stability of radical formed upon $\text{C – H}$ bond cleavage via hyperconjugation.

The phenomenon of hyperconjugation refers to donation of $\text{σ}$ electrons into the partly vacant $p$ orbital lobes of radical carbon. More will be number of $\text{σ}$ orbital capable of donation of electrons more is the stabilization.